Discrete photoelectrodes with dyes having different absorption wavelengths for efficient cobalt-based tandem dye-sensitised solar cells

Phuong Ho,Jae Hong Kim,Yong Hui Lee,Suresh Thogiti

doi:10.1038/s41598-017-02480-y

Abstract

A pn-tandem dye-sensitised solar cell (pn-DSSC) employing a set of sensitisers with complementary absorption spectra and a less-corrosive cobalt-based electrolyte is presented. We applied three organic sensitisers (denoted C343, DCBZ, and SQ) featuring different absorption wavelengths for the p-DSSC, while keeping the n-DSSC sensitiser (denoted DCA10CN2) constant. Characterisation of the Co+2/+3-based DSSC devices revealed that SQ dye, with a longer absorption wavelength, showed broader spectra and increased photocurrent activity in the visible and near-infrared region compared to the other two devices with C343 and DCBZ in the pn-DSSCs. As a result, the short-circuit current density increased significantly to 4.00 mA cm−2, and the devices displayed overall power conversion efficiencies of as high as 1.41%, which is comparable to that of the best pn-DSSCs in the literature. Our results demonstrate that complementary absorption between the two photoelectrodes is important for enhancing the photovoltaic performance of pn-DSSCs.

Highlights

Dye-sensitised solar cells (DSSCs) incorporating mesoporous-network-based photoelectrodes are often suggested as a low-cost replacement for conventional silicon-based solar cells[1]
Using p-type dye sensitisers with different absorption maxima yields dyes that absorb longer wavelengths that complement those of the state-of-the-art photoanodes in tandem cells (Figs 1 and 2)
In an attempt to improve the efficiency of DSSCs, we investigated tandem pn-tandem dye-sensitised solar cell (pn-DSSC) using an optically dilute and less-corrosive cobalt-based redox electrolyte

Summary

Introduction

Dye-sensitised solar cells (DSSCs) incorporating mesoporous-network-based photoelectrodes are often suggested as a low-cost replacement for conventional silicon-based solar cells[1]. A dye-coated photocathode (p-type) with absorption complementary to that of the photoanode (n-type) would enable fabrication of pn-type tandem cells, where the Pt-based counter electrode found in conventional DSSCs (n-type) is replaced with a dye-sensitised p-type semiconductor[10, 11]. This allows more photons to be converted more efficiently. Achieving high-PCE pn-DSSCs entails the development of (i) novel photocathodes with a higher ionisation potential to improve the photovoltage, (ii) optically transparent and non-corrosive electrolytes, and (iii) sensitisers with complementary absorption spectra. Among photocathodes fabricated using three well known dyes, C34318–27, DCBZ16, 26, and SQ16, 68, an SQ-based photocathode yielded near-IR absorption by the photocathode and complementary absorption between the photoanode and photocathode in pn-DSSCs (Fig. 2)

Objectives

Methods

Results

Conclusion